INDIANAPOLIS (AP) — A fire engulfed a sprawling mixed-use building near downtown Indianapolis filled with tires and wooden pallets Saturday, producing a towering pillar of black smoke that prompted the evacuation of a five-block area surrounding the structure, authorities said.

Capt. Rita Burris of the Indianapolis Fire Department said about 100 firefighters from six departments were battling the fire that was consuming the two-story brick building about one mile southwest of the city’s downtown.

The building was rocked by numerous explosions that Burris said are believed to have been small propane tanks exploding from the heat of the fire.

She said the building houses tire- and pallet-recycling businesses, a bicycle shop and storage facilities, but none were believed to have been open when the fire was reported Saturday afternoon.

The blaze produced such a large plume of black smoke that firefighters ordered the evacuation of a five-block area around the building due to the health threat posed by the smoke, Burris said.

Early Saturday evening, Burris said crews were probably hours away from bringing the fire under control and that firefighters might order additional evacuations if the wind shifted. The fire was reported about 1 p.m. EDT and was still burning seven hours later.

She said the only injury has been a firefighter who hurt his knee at the scene.

Because of the scope of the fire, crews had to ask the local water department twice to boost water pressure so that they could get enough water to start dousing the flames, Burris said.

Fire crews were expected to remain at the scene through Saturday night working to put out the fire. Once the fire is out, Burris said crews will remain on the scene for several days to make sure the blaze doesn’t ignite again.

Indianapolis Metropolitan Police spokesman Chris Wilburn said the businesses inside the building contain about 85,000 tires, 60,000 wood pallets and a 500-gallon propane tank that’s about one-quarter full. He said firefighters were directing water toward the tank to prevent it from exploding.

The U.S. Environmental Protection Agency was at the scene monitoring air quality, while officials from the Bureau of Alcohol, Tobacco, Firearms and Explosives and the local health department have also responded, Wilburn said.

Reserve officers were called to the scene Saturday to help with the evacuation and move residents from their homes to shelters.

“At this point they’re doing the best they can to get it under control,” Wilburn said.